Method for processing semiconductor substrate

ABSTRACT

A method of processing a semiconductor substrate includes a step of forming a trench ( 16 ) in a surface of the substrate, by etching the substrate (W), and a step of rounding a corner ( 10 ) of the substrate formed at a mouth of the trench ( 16 ), by heat-processing the substrate (W). The step of rounding the corner ( 10 ) includes a first heat process performed in a hydrogen gas atmosphere with a process temperature T set to be 850° C.&lt;T&lt;1,050° C., and a process pressure P set to be 0.01 kPa&lt;P&lt;30 kPa.

TECHNICAL FIELD

The present invention relates to a method of processing a semiconductorsubstrate, a method of forming a device isolation region for separatinga device region on a semiconductor substrate, a method of manufacturinga semiconductor device having a gate structure on a device regionadjacent to a device isolation region, and a heat-processing apparatusfor a semiconductor substrate. More specifically, the present inventionprovides an improved trench structure according to the methods describedabove.

BACKGROUND ART

Where a number of device units, such as transistors, are arrayed on asemiconductor substrate (silicon substrate or compound semiconductorsubstrate), the device units are respectively formed in device regionsthat are electrically isolated from each other by device isolationregions. As a device isolation region, there is known a trench isolationstructure that includes a trench formed in the surface of asemiconductor substrate, and an insulator, such as silicon oxide film,filling the trench.

FIG. 8 is an enlarged sectional view showing a conventional trenchisolation structure. As shown in FIG. 8, trenches are formed bypattern-etching the surface of a semiconductor substrate W, and each ofthem is filled with an insulator 2, such as a silicon oxide film. Theinsulators 2 surround device regions 4 to electrically isolate thedevice region 4 from each other. FIG. 8 shows, as an example, the gateoxide film 6 and gate electrode 8 of a MOS transistor formed in eachdevice region 4 (FIG. 8 shows a sectional view in the channel widthdirection).

As described above, the surface of a semiconductor substrate W is etchedto form the trenches of device isolation regions. With this etching,each of substrate surface corners 10, i.e., the trench edges (asubstrate corner is formed between a device region and a deviceisolation region), has an angle of, e.g., about 90 degrees. Where thecorners 10 have such an angle, the oxidation rate tends to be lower atthe corners 10, when an oxide film (gate oxide film 6) is formed on thesurface of the semiconductor substrate W. As a consequence, the gateoxide film 6 has a film thickness H1 at the corners 10 far smaller thanthat at the other portions. If the gate oxide film 6 has a smaller filmthickness locally at the corners 10, leakage current is generated there,because electrical field concentration occurs at the corners 10.

One countermeasure to this problem is a processing method for roundingthe trench edge corners of the device isolation regions, so as toprevent the gate oxide film from being thinner at the corners 10. FIGS.9A to 9F are sectional views showing a series of steps in a conventionalsemiconductor substrate processing method for rounding the trench edgecorners of device isolation regions. FIG. 10 is an enlarged sectionalview showing a conventional trench isolation structure formed at the endof the processing method shown in FIGS. 9A to 9F.

First, as shown in FIG. 9A, a first insulating film 12 consisting of,e.g., a silicon oxide film, and a second insulating film 14 consistingof, e.g., a silicon nitride film are formed and laminated in this orderon the surface of a semiconductor (silicon) substrate W. Then, as shownin FIG. 9B, trenches (grooves) 16 are formed in a predetermined patternby etching, such that each trench 16 extends from the surface of thefirst and second insulating films 12 and 14 into the semiconductorsubstrate W.

Then, an oxidizing process is performed at a high temperature in anoxygen atmosphere, thereby oxidizing the side surfaces of the trenches16 exposed to the oxygen atmosphere, to form a thin liner oxide film 18thereon, as shown in FIG. 9C. With the liner oxide film 18 thus formed,each of the substrate surface corners 10, i.e., the edges of thetrenches 16, is provided with a curved portion 18A of the liner oxidefilm 18 that is continuously disposed thereon as a curved projection.

Then, as shown in FIG. 9D, a silicon oxide film 20 is deposited by CVD(Chemical Vapor Deposition) over all the device regions and deviceisolation regions to fill the trenches 16. Then, as shown in FIG. 9E,the silicon oxide film 20 is etched to a position where the uppermostsecond insulating film 14 is exposed.

Then, as shown in FIG. 9F, the second insulating film 14 and firstinsulating film 12 are sequentially removed by etching, while leavingthe silicon oxide film 20 filling the trenches 16. As a consequence, thedevice regions are electrically isolated from each other by the deviceisolation regions. The curved portion 18A of the liner oxide film 18remains curved. Thereafter, as described above, gate oxide films 6 andgate electrodes 8 (see FIG. 10) are formed to fabricate transistors.

According to the method described above, as shown in FIG. 10, each ofthe corners 10, i.e., the trench edges, is provided with the curvedportion 18A of the liner oxide film 18 continuously disposed thereon. Asa consequence, the gate oxide film 6 has a sufficient film thickness H2at the corners 10 to prevent leakage current from generating, as that atthe other portions.

Incidentally, since semiconductor integration circuits are required tobe more integrated and miniaturized in recent years, the trenches 16need to have a smaller width. For example, the trenches 16 need to havea width L1 (see FIG. 9B) as small as about 0.1 μm. In this case, wherethe liner oxide film 18 is formed, as described above, the mouth of eachtrench 16 becomes very narrow, even if the liner oxide film 18 has asmall film thickness of, e.g., about 15 nm. As a consequence, it becomesdifficult to sufficiently fill the trenches 16 with the silicon oxidefilm 20 in a subsequent step, thereby creating voids in the trenches 16.

Jpn. Pat. Appln. KOKAI Publication No. 2000-58780 discloses anotherprocessing method for rounding substrate surface corners 10, i.e., thetrench edges, without forming the liner oxide film 18 (see pages 13 to15, FIGS. 50 to 66). In this processing method, after trenches 16 areformed, as shown in FIG. 9B, the entire semiconductor substrate W isheat-treated at a high temperature in a hydrogen atmosphere. By doingso, atomic migration is thermally caused in the silicon surface, andthereby rounds the corners 10.

However, it has been found by the present inventors' experiments, thatthe processing method disclosed in this publication has insufficienciesin the process conditions, which bring about other problems. Examples ofthe problems are that surface roughness excessively occurs on the sidesurfaces of the edges of trenches 16, and migration excessively occursand considerably deforms the shape of trenches 16.

DISCLOSURE OF INVENTION

An object of the present invention is to provide an improved trenchstructure, in a method of processing a semiconductor substrate, a methodof forming a device isolation region for separating a device region on asemiconductor substrate, a method of manufacturing a semiconductordevice having a gate structure on a device region adjacent to a deviceisolation region.

According to a first aspect of the present invention, there is provideda method of processing is a semiconductor substrate, the methodcomprising:

forming a trench in a surface of the substrate, by etching thesubstrate; and

rounding a corner of the substrate formed at a mouth of the trench, byheat-processing the substrate, wherein rounding the corner comprises afirst heat process performed in a hydrogen gas atmosphere with a processtemperature T set to be 850° C.<T<1,050° C., and a process pressure Pset to be 0.01 kPa<P<30 kPa.

According to a second aspect of the present invention, there is provideda method of forming a device isolation region for separating a deviceregion on a semiconductor substrate, the method comprising:

forming a process insulating film on the substrate;

forming a trench extending from a surface of the process insulating filminto the substrate, by etching a portion corresponding to the deviceisolation region;

rounding a corner of the substrate formed at a boundary between thetrench and the device region, by heat-processing the substrate whileleaving the process insulating film disposed on the device region,wherein rounding the corner comprises a first heat process performed ina hydrogen gas atmosphere with a process temperature T set to be 850°C.<T<1,050° C., and a process pressure P set to be 0.01 kPa<P<30 kPa;

performing, subsequently to the first heat process, a second heatprocess to cover a surface inside the trench with a protection oxidefilm, by oxidizing the substrate while heating the substrate;

forming a deposition film of an insulator in the trench and on thedevice region while leaving the process insulating film disposed on thedevice region; and

removing both the deposition film and the process insulating film on thedevice region, thereby leaving an filling insulator in the trench, andforming an exposed surface of the substrate in the device region.

According to a third aspect of the present invention, there is provideda method of manufacturing a semiconductor device including a gatestructure on a device region adjacent to a device isolation region, themethod comprising:

forming a process insulating film on a semiconductor substrate used as asubstrate of the semiconductor device;

forming a trench extending from a surface of the process insulating filminto the substrate, by etching a portion corresponding to the deviceisolation region;

rounding a corner of the substrate formed at a boundary between thetrench and the device region, by heat-processing the substrate, whereinrounding the corner comprises a first heat process performed in ahydrogen gas atmosphere with a process temperature T set to be 850°C.<T<1,050° C., and a process pressure P set to be 0.01 kPa<P<30 kPa;

performing, subsequently to the first heat process, a second heatprocess to cover a surface inside the trench with a protection oxidefilm, by oxidizing the substrate while heating the substrate;

forming a filling insulator in the trench;

forming an exposed surface of the substrate in the device region, afterforming the filling insulator; and

forming a gate insulating film and a gate electrode in this order overthe exposed surface and the corner.

According to a fourth aspect of the present invention, there is provideda heat-processing apparatus for a semiconductor substrate, the apparatuscomprising:

a process chamber configured to accommodate the substrate;

a support member configured to support the substrate in the processchamber;

a heater configured to heat the substrate accommodated in the processchamber;

a gas supply system configured to supply a process gas into the processchamber;

an exhaust system configured to exhaust the process chamber; and

a controller configured to control an operation of the processingapparatus,

wherein the controller is set to successively perform first and secondheat processes on the substrate, which has been provided with a trenchformed in a surface thereof, in the process chamber,

the first heat process is performed to round a corner of the substrateformed at a mouth of the trench, in a hydrogen gas atmosphere with aprocess temperature T set to be 850° C.<T<1,050° C., and a processpressure P set to be 0.01 kPa<P<30 kPa, and

the second heat process is performed to cover a surface inside thetrench with a protection oxide film, by oxidizing the substrate whileheating the substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view schematically showing a verticalheat-processing apparatus for performing a method of manufacturing asemiconductor device according to an embodiment of the presentinvention;

FIGS. 2A to 2H are sectional views showing a series of steps in a methodof manufacturing a semiconductor device according to an embodiment ofthe present invention (including a method of forming a device isolationregion and a method of processing a semiconductor substrate);

FIG. 3 is a graph showing change in the temperature of processing stepsperformed, using the heat-processing apparatus shown in FIG. 1;

FIG. 4 is a graph showing change in the temperature of semiconductorsubstrates, used in an evaluation experiment in a step of roundingcorners;

FIG. 5 is a graph showing other change in the temperature ofsemiconductor substrates, used in the evaluation experiment in the stepof rounding corners;

FIG. 6 is a graph showing evaluation results in terms of therelationship between process temperature and process pressure in thestep of rounding corners;

FIGS. 7A to 7C are schematic views showing change in the shape of atrench;

FIG. 8 is an enlarged sectional view showing a conventional trenchisolation structure;

FIGS. 9A to 9F are sectional views showing a series of steps in aconventional semiconductor substrate processing method for rounding thetrench edge corners of device isolation regions; and

FIG. 10 is an enlarged sectional view showing a conventional trenchisolation structure formed at the end of the processing method shown inFIGS. 9A to 9F.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described withreference to the accompanying drawings. In the following description,the constituent elements having substantially the same function andarrangement are denoted by the same reference numerals, and a repetitivedescription will be made only when necessary.

FIG. 1 is a sectional view schematically showing a verticalheat-processing apparatus for performing a method of manufacturing asemiconductor device according to an embodiment of the presentinvention.

As shown in FIG. 1, this vertical heat-processing apparatus 22 has aprocess container 24 made of quartz and shaped as cylindrical columnwith a ceiling. The bottom of the process container 24 is opened to forma port 26 with a flange 28 formed around it for connection. The processcontainer 24 is surrounded by a cylindrical heat insulator 32, which isprovided with a heater 30 or heating means disposed on the inner side,thereby constituting a furnace.

A hydrogen feed nozzle 34 for feeding hydrogen and an oxygen feed nozzle36 for feeding oxygen are disposed to penetrate a lower portion of thesidewall of the process container 24. The nozzles 34 and 36 extend alongthe inner surface of the sidewall of the process container 24 to theceiling, so as to spout gases therefrom at flow rates controlled asneeded. Nozzles 37 for feeding TEOS (tetraethylorthosilicate) and O₃,which are used when a CVD film of an insulator is formed, are alsodisposed to penetrate a lower portion of the sidewall of the processcontainer 24 (although TEOS and O₃ are supplied through differentnozzles, they are shown as a single nozzle). The nozzles 34, 36, and 37are connected to a gas supply section 33.

An exhaust port 38 having a relatively large diameter is formed in alower portion of the sidewall of the process container 24, and isconnected to an exhaust section 39 including an exhaust pump or thelike. The exhaust section 39 exhausts the atmosphere inside the processcontainer 24 to set the interior at a predetermined vacuum level.

A stainless steel base plate 40 is disposed to support the outer portionof the flange 28 of the process container 24, so as to support theentirety of the process container 24. The port 26 at the bottom of theprocess container 24 is opened and closed by a cap 44, which is made ofquartz or stainless steel and moved up and down by an elevatingmechanism 42. A quartz support boat 46, on which semiconductorsubstrates W are placed at a predetermined pitch in the verticaldirection, is placed on the cap 44 through a cylindrical holder 48. Thesupport boat 46 is loaded into and unloaded from the process container24 by moving the cap 44 up and down. The support boat 46 may be rotatedor not rotated.

The entire operation of the vertical heat-processing apparatus 22 iscontrolled in accordance with a program preset in a control sectionCONT. Under the control of the control section CONT, a predeterminedprocess is performed in the heat-processing apparatus 22, for example,as follows.

First, semiconductor substrates W are transferred onto the support boat46 in an unload state where the elevating mechanism 42 is placed at alower position. For example, the support boat 46 is designed to stack 50to 100 8-inch wafers with a gap therebetween. At this time, thesesemiconductor substrates W have already been subjected to apredetermined process in a previous step, as described later. Then, thecap 44 is moved up along with the support boat 46 by the elevatingmechanism 42 to load the support boat 46 through the bottom port 26 intothe process container 24. Then, the bottom port 26 of the processcontainer 24 is airtightly closed by the cap 44 to hermetically seal theprocess container 24.

Then, the temperature of the heater 30 is raised to heat thesemiconductor substrates W to a predetermined process temperature. Also,while the interior of the process container 24 is exhausted, a necessaryprocess gas, such as hydrogen gas or oxygen gas, is supplied at a flowrate controlled as needed. By doing so, a predetermined heat process isperformed while the process pressure in the process container 24 is keptat a predetermined pressure. In this heat-processing apparatus 22, arounding step and a surface oxidation step both described later aresequentially performed in practice. Furthermore, in this heat-processingapparatus 22, a step of forming a CVD film of an insulator is performedsubsequently to these steps.

Next, with reference to FIGS. 1 to 3, an explanation will be given of amethod of manufacturing a semiconductor device according to anembodiment of the present invention (including a method of forming adevice isolation region and a method of processing a semiconductorsubstrate), which is performed under the control of the control sectionCONT. FIGS. 2A to 2H are sectional views showing a series of steps in amethod of manufacturing a semiconductor device according to anembodiment of the present invention (including a method of forming adevice isolation region and a method of processing a semiconductorsubstrate). FIG. 3 is a graph showing change in the temperature ofprocessing steps performed, using the heat-processing apparatus shown inFIG. 1.

First, as shown in FIG. 2A, a first insulating film 12 formed of, e.g.,a silicon oxide film and a second insulating film 14 formed of, e.g., asilicon nitride film are deposited in this order on the surface of asemiconductor substrate W consisting of silicon or a compoundsemiconductor. The first insulating film 12 and second insulating film14 are not limited to these examples. For example, the first insulatingfilm 12 may be formed of an oxynitride film, or the second insulatingfilm 14 may be formed of an oxynitride film.

Then, as shown in FIG. 2B, trenches (grooves) 16 are formed by etchingportions to be device isolation regions, from the surface of the secondinsulating film 14 into the semiconductor substrate W. In thisembodiment, for example, plasma is used to etch the first and secondinsulating films 12 and 14 and the semiconductor substrate W, so as toform the trenches 16 in a predetermined pattern. The width L1 of eachtrench 16 is set at, e.g., about 0.1 μm.

Then, semiconductor substrates W with trenches 16 thus formed in theirsurfaces are transferred into the process container 24 of theheat-processing apparatus 22 described with reference to FIG. 1. Then,the semiconductor substrates W are subjected to a rounding step (firstheat process) RS shown in FIG. 2C, and a surface oxidation step (secondheat process) OS shown in FIG. 2D, conducted in series in this processcontainer 24. Furthermore, they may be subsequently subjected to a stepof forming a CVD film of an insulator described later, conducted as athird heat process. As shown in FIGS. 2C to 2D, these steps areperformed while the first and second insulating films 12 and 14 remainon device regions.

More specifically, as also shown in FIG. 3, in the rounding step RS, thesemiconductor substrates W are transferred (loaded) into the processcontainer 24 heated at, e.g., about 300° C., and then hydrogen gasstarts being supplied into the process container 24. The semiconductorsubstrates W are quickly heated to about 850° C. and kept at thistemperature for about 5 minutes to stabilize the temperature of thesemiconductor substrates W. The process pressure is set at, e.g., about1 kPa.

After the substrate temperature becomes stable, the temperature of thesemiconductor substrates W is raised to a temperature of 850° C. to1,050° C., e.g., 1,000° C. This completes the rounding step RS. Asdescribed later, where the temperature of the semiconductor substrates Wis raised to 1,000° C., atomic migration is thermally caused in thematerial surfaces of the semiconductor substrate W, thereby changing thesurfaces into a deformable state, in a moment when the semiconductorsubstrates W are exposed to this temperature. As a consequence, as shownin FIG. 2C, substrate surface corners 10, i.e., the edges of thetrenches 16, are rounded with a predetermined curvature, and therounding step RS is thereby completed. In this step, the flow rate ofhydrogen gas is set at, e.g., about 2 to 30 liters/minute, depending onthe volume of the process container 24.

After the rounding step RS is thus completed, i.e., the temperature ofthe semiconductor substrates W is raised to 1,000° C., which is anexample of the process temperature, the surface oxidation step OSfollows. In the surface oxidation step OS, the temperature of thesemiconductor substrates W is maintained as it is, i.e., at 1,000° C.Hydrogen and oxygen are supplied at the same time as process gases. Theflow rate of hydrogen is set at, e.g., about 1 liter/minute, and theflow rate of oxygen is set at, e.g., about 2 liters/minute. The processpressure is set at a very low pressure, which is not more than 133 Pa (1Torr) and not less than 1.33 Pa (0.01 Torr).

In other words, the surface oxidation step OS is performed by aso-called low pressure radical oxidizing process (LPRO: Low PressureRadical Oxidation), (for example, it is disclosed in U.S. Pat. No.6,599,845). In the low pressure radical oxidizing process, water vaporis generated from oxygen radicals and hydroxy radicals, and uniformlyoxidizes the semiconductor substrate surface and more specifically thesilicon surface exposed inside the trenches 16. As a consequence, a thinprotection oxide film 49 consisting of SiO₂ is formed, such that it hasa thickness of, e.g., about 6 nm in a case where the process isperformed for about 6 minutes. The protection oxide film 49 protects theinner surface of the trenches 16, which has been damaged by the plasmaetching shown in FIG. 2B. In this step, gas supply rates, processtemperature, and process pressure may be adjusted in ranges that allowthe low pressure radical oxidizing process described above to beperformed.

After the surface oxidation step OS is thus completed, the semiconductorsubstrates W are unloaded from the process container 24 to the outside.Then, the same processing apparatus or another processing apparatus isused to perform a filling step on the semiconductor substrates W by,e.g., a plasma CVD process, such as a HDP (High Density Plasma) processor TEOS/O₃ process. In this step, as shown in FIG. 2E, the trenches 16are filled with an insulator 50, such as silicon oxide, and a depositionfilm of the insulator 50 is formed over the entire surface of thesubstrate (i.e., including the surface of the device regions).

After the filling step is thus completed, as shown in FIG. 2F, anetching process or CMP process is performed to remove the insulatordeposition film 50, so as to expose the surface of the second insulatingfilm 14. Since the insulator deposition film 50 consists of siliconoxide while the second insulating film 14 consists of silicon nitride, asufficiently large etching selectivity is obtained between the twomaterials. As a consequence, the etching of the insulator depositionfilm 50 can be easily stopped at a position corresponding to the secondinsulating film 14.

Then, as shown in FIG. 2G, the insulator deposition film 50, secondinsulating film 14, and first insulating film 12 on the device regionsare removed in this order by etching processes. In this step, the topportion of the insulator 50 is slightly removed. As a consequence, thefilling insulator 50 is left in the trenches 16, and the exposed surfaceof the substrate W is obtained in the device regions. In this state, thedevice regions are separated and electrically isolated by the deviceisolation regions each formed of the trench 16 filled with the insulator50.

Then, as shown in FIG. 2H, gate insulating films 6 and gate electrode 8are sequentially formed in a predetermined pattern to cover portionseach extending over the exposed surface and the corners 10 of eachdevice region. Then, an impurity is diffused into the device regions toform source and drain layers (not shown) in the surface of each deviceregion, while using, as a mask, gate structures each formed of theinsulating film 6 and gate electrode 8 and having a predetermined shape.As a consequence, MOS transistors (semiconductor devices) 52 arefabricated (FIG. 2H shows a sectional view in the channel widthdirection).

In the semiconductor devices 52 thus fabricated, as shown in FIG. 2C,the substrate surface corners 10, i.e., the edges of the trenches 16,are rounded. Accordingly, the gate oxide film 6 (see FIGS. 2H and 10) isprevented from being locally thinner, thereby suppressing leakagecurrent. In addition, since the thick liner oxide film 18 shown in FIG.9C need not be formed on the inner surface of the trenches 16, thetrenches 16 can be filled sufficiently, avoiding creation of voidstherein. Since the protection film 49 shown in FIG. 2D is far thinnerthan the liner oxide film 18, it does not seriously affect the width L1of the trenches 16 (see FIG. 2B).

Next, an explanation will be given of an evaluation experiment onprocess conditions in the step of rounding the corners 10, as shown inFIG. 2C.

FIGS. 4 and 5 are graphs showing change in the temperature ofsemiconductor substrates, used in the evaluation experiment in the stepof rounding corners. FIG. 6 is a graph showing evaluation results interms of the relationship between process temperature and processpressure in the step of rounding corners.

FIGS. 7A to 7C are schematic views showing change in the shape of atrench. In FIG. 6, the symbols “◯” denote good results, and the symbols“×” denote bad results.

In the evaluation experiment, the process temperature (ultimate maximumvalue) was set at different values at regular intervals of 50° C. in arange of 850° C. to 1,050° C. The process pressure was set at differentvalues in a range of 0.05 kPa to 30 kPa. As a process gas, only hydrogengas was supplied, as descried above.

The temperature of the semiconductor substrates W was controlled, asfollows. Specifically, as shown in FIG. 4, semiconductor substrates Wwere loaded into the process container 24 (see FIG. 1) heated at about300° C. in advance. The semiconductor substrates W were quickly heatedto 850° C. and kept at this temperature for about 5 minutes to stabilizethe temperature. Then, the semiconductor substrates W were heated todifferent ultimate maximum values in a range of 850° C. to 1,050° C.,and then quickly (in a moment) cooled. After the semiconductorsubstrates W are cooled down, the surfaces of the substrates, such asthe corners 10 of the trenches 16, were observed.

The hydrogen gas was kept supplied until the substrate temperature waslowered to about 300° C. The hydrogen gas flow is intended to preventsilicon atoms from being dissociated from the silicon surface. Because,if the supply of hydrogen gas is stopped when the substrates are at ahigh temperature, the interior of the process container becomes a highvacuum, thereby causing silicon atoms to be dissociated from the siliconsurface.

As shown in FIG. 6, the results of the evaluation experiment revealedthat, where the process temperature was set at 850° C., no good resultswere obtained regardless of the process pressure. It is presumed that,this was so, because 850° C. was too low as heating temperature tosufficiently cause migration. In this case, as shown in FIG. 7A, theshape of corners 10 of the trenches 16 remained angular.

Also, where the process temperature was set at 1,050° C., preferableresults were not obtained regardless of the process pressure. It ispresumed that, this was so, because 1,050° C. was too high as heatingtemperature, thereby causing excessive migration and promotingdeformation. In this case, as shown in FIG. 7C, the corners 10 of thetrenches 16 were rounded, but a large wide-bottomed recess 54 was formedat the bottom of the trenches 16. Since such a recess 54 may cause avoid, it is not preferable.

On the other hand, where the process temperature was set at 950° C. andthe process pressure was set at a value of 0.05 kPa to 10 kPa, and wherethe process temperature was set at 975° C. or 1,025° C. and the processpressure was set at a value of 0.05 kPa to 20 kPa, good results wereobtained. In these cases, as shown in FIG. 7B, the corners 10 of thetrenches 16 were suitably rounded, without forming the large recess 54shown in FIG. 7C. Accordingly, it has been found that these conditionsfall into the most pertinent scope.

Where the process temperature was set at 950° C. and the processpressure was set at 20 kPa, and where the process temperature was set at975° C. or 1,025° C. and the process pressure was set at 30 kPa, thecorners 10 were not suitably rounded.

Where the process temperature was set at 900° C. and the processpressure was set at 0.05 kPa or 0.1 kPa, the corners 10 were suitablyrounded, but remarkable surface roughness was observed on its surface.Accordingly, it has been found that these conditions do not fall intothe most pertinent scope, but are useful for rounding the corners 10 tosome extent.

Where the process temperature was set at 900° C. and the processpressure was set at 1 kPa, the corners 10 of the trenches 16 were notrounded but maintained the shape, as shown in FIG. 7A. In this respect,it was found that, where the substrates were kept at 900° C. for 20minutes, as shown in FIG. 5, the corners 10 of the trenches 16 weresuitably rounded, as shown in FIG. 7B. This keeping time of 20 minutesis a limit value, in consideration of the throughput of the substrateprocess.

Where the process temperature was set at 900° C. and the processpressure was set at 5 kPa or 10 kPa, the corners 10 were not roundedeven after the substrates were kept at that temperature for 20 minutes.In the present heat-processing apparatus, about 0.01 kPa is the lowestpressure that can be formed by vacuum-exhausting it while supplyinghydrogen gas. Accordingly, the lowest process pressure of this processis also about 0.01 kPa.

Based on the results described above, it has been found that thefollowing conditions are preferably used in the step of rounding thecorners 10. Specifically, the process temperature T is set to be 850°C.<T<1,050° C., and the process pressure P is set to be 0.01 kPa<P<30kPa. More preferably, the process temperature T is set to be 900°C.≦T≦1,025° C., and the process pressure P is set to be 0.05 kPa≦P≦20kPa. Specifically, the symbols “◯” in FIG. 6 show a scope defined bynecessary and sufficient conditions. In the step of rounding the corners10 and the step of forming the protection film 49 by oxidation shown inFIGS. 2C and 2D, the total period of time for the substrates W to bekept at the highest temperature is set at 1 to 15 minutes, andpreferably at 1 to 5 minutes.

The heat-processing apparatus for performing the heat process is notlimited to that shown in FIG. 1, but may be a heat-processing apparatuswith a double-tube process container, or a heat-processing apparatus ofthe type that processes substrates one by one. The size of thesemiconductor substrate may be any one of 6-inch, 8-inch, 12-inch, andso forth.

INDUSTRIAL APPLICABILITY

With a method of manufacturing semiconductor devices according to theembodiments described above (including a method of forming a deviceisolation region and a method of processing a semiconductor substrate),it is possible to sufficiently round substrate surface corner, i.e., thetrench edges, without deforming the trench groove shape, even if thetrench width is reduced.

1. A method of processing a semiconductor substrate, the methodcomprising: forming a trench in a surface of the substrate, by etchingthe substrate; rounding a corner of the substrate formed at a mouth ofthe trench, by heat-processing the substrate, wherein rounding thecorner comprises a first heat process performed in a hydrogen gasatmosphere with a process temperature T set to be 850° C.<T<1,050° C.,and a process pressure P set to be 0.01 kPa<P<30 kPa; and performing,subsequently to the first heat process, a second heat process to cover asurface inside the trench with a protection oxide film, by oxidizing thesubstrate while heating the substrate, wherein the second heat processis performed in a mixed gas atmosphere of oxygen and hydrogen with aprocess pressure set to be 133 Pa or less.
 2. The method according toany one of claim 1, wherein the process temperature T is set to be 900°C.≦T≦1,025° C., and the process pressure P is set to be 0.05 kPa≦P≦20kPa.
 3. A method of forming a device isolation region for separating adevice region on a semiconductor substrate, the method comprising:forming a process insulating film on the substrate; forming a trenchextending from a surface of the process insulating film into thesubstrate, by etching a portion corresponding to the device isolationregion; rounding a corner of the substrate formed at a boundary betweenthe trench and the device region, by heat-processing the substrate whileleaving the process insulating film disposed on the device region,wherein rounding the corner comprises a first heat process performed ina hydrogen gas atmosphere with a process temperature T set to be 850°C.<T<1,050° C., and a process pressure P set to be 0.01 kPa<P<30 kPa;performing, subsequently to the first heat process, a second heatprocess to cover a surface inside the trench with a protection oxidefilm, by oxidizing the substrate while heating the substrate, whereinthe second heat process is performed in a mixed gas atmosphere of oxygenand hydrogen with a process pressure set to be 133 Pa or less; forming adeposition film of an insulator in the trench and on the device regionwhile leaving the process insulating film disposed on the device region;and removing both the deposition film and the process insulating film onthe device region, thereby leaving an filling insulator in the trench,and forming an exposed surface of the substrate in the device region. 4.The method according to claim 3, wherein the first and second heatprocesses are performed in a process chamber in which a process offorming the deposition film of an insulator is performed.
 5. The methodaccording to claim 3, wherein the process temperature T is set to be900° C.≦T≦1,025° C., and the process pressure P is set to be 0.05kPa≦P≦<20 kPa.
 6. A method of manufacturing a semiconductor deviceincluding a gate structure on a device region adjacent to a deviceisolation region, the method comprising: forming a process insulatingfilm on a semiconductor substrate used as a substrate of thesemiconductor device; forming a trench extending from a surface of theprocess insulating film into the substrate, by etching a portioncorresponding to the device isolation region; rounding a corner of thesubstrate formed at a boundary between the trench and the device region,by heat-processing the substrate, wherein rounding the corner comprisesa first heat process performed in a hydrogen gas atmosphere with aprocess temperature T set to be 850° C.<T<1,050° C., and a processpressure P set to be 0.01 kPa<P<30 kPa; performing, subsequently to thefirst heat process, a second heat process to cover a surface inside thetrench with a protection oxide film, by oxidizing the substrate whileheating the substrate, wherein the second heat process is performed in amixed gas atmosphere of oxygen and hydrogen with a process pressure setto be 133 Pa or less; forming a filling insulator in the trench; formingan exposed surface of the substrate in the device region, after formingthe filling insulator; and forming a gate insulating film and a gateelectrode in this order over the exposed surface and the corner.
 7. Themethod according to claim 6, wherein the process temperature T is set tobe 900° C.≦T≦1,025° C., and the process pressure P is set to be 0.05kPa≦P≦<20 kPa.
 8. The method according to claim 6, wherein rounding thecorner is performed while leaving the process insulating film disposedon the device region, and forming the filling insulator is performed byforming a deposition film of an insulator in the trench and on thedevice region while leaving the process insulating film disposed on thedevice region, and then removing both the deposition film and theprocess insulating film on the device region.
 9. The method according toclaim 8, wherein the first and second heat processes are performed in aprocess chamber in which a process of forming the deposition film of aninsulator is performed.